This application claims the benefit of Korean Patent Application No. 2001-87595, filed on Dec. 28, 2001, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a LCD device having a scattering layer and a fabricating method thereof.
2. Discussion of the Related Art
Flat panel display (FPD) devices having a small size, lightweight, and low power consumption have been a subject of recent research in the advent of the information age. FPD devices may be classified into two types depending on whether the device emits or receives light. One type is a light-emitting type display device that emits light to display images, and the other type is a light-receiving type display device that uses an external light source to display images. Plasma display panels (PDPs), field emission display (FED) devices, and electroluminescent (EL) devices are examples of the light-emitting type display devices. Liquid crystal display (LCD) devices are examples of the light-receiving type display device. Among many kinds of FPD devices, LCD devices are widely used for notebook computers and desktop monitors because of their excellent characteristics of resolution, color display and display quality.
Generally, LCD devices include an upper substrate and a lower substrate facing each other with liquid crystal molecules interposed therebetween. Each substrate has an electrode on the inner surface thereof. An electric field is generated by applying a voltage to the electrodes, thereby driving the liquid crystal molecules to display images in accordance with the light transmittance.
Since LCD devices do not emit light, an additional light source is necessary. Accordingly, LCD devices display images by disposing a backlight at a backside thereof and transmitting light from the backlight. Here, electric field-generating electrodes of LCD devices are usually made of a transparent conductive material and the two substrates are usually transparent. This kind of LCD device is referred to as a transmission type LCD device or a transmissive LCD device. Even though a transmissive LCD device can display bright images under a dark environment due to an artificial light source such as a backlight, the transmissive LCD device has a disadvantage of high power consumption due to the backlight.
To remedy this disadvantage, a reflective (or reflection type) LCD device is suggested. The reflective LCD device displays images by reflecting external natural or artificial light, thereby having a low power consumption compared with the transmissive LCD device. In the reflective LCD device, a lower electric field-generating electrode is made of a conductive material having high reflectance and an upper electric field-generating electrode is made of a transparent conductive material so that external light can be transmitted through the upper electric field-generating electrode.
FIG. 1 is a schematic cross-sectional view of a related art reflective LCD device. In FIG. 1, first and second substrates 11 and 21 are spaced apart from each other. A gate electrode 12 and a gate line (not shown) are formed on an inner surface of the first substrate 11 and a gate insulating layer 13 is formed on the gate electrode 12. An active layer 14, an ohmic contact layer 15a and 15b, and source and drain electrodes 16b and 16c are sequentially formed on the gate insulating layer 13 over the gate electrode 12 and constitutes a thin film transistor (TFT) xe2x80x9cTxe2x80x9d with the gate electrode 12. A data line 16a of the same material as the source and drain electrodes 16b and 16c is also formed on the gate insulating layer 13 and connected to the source electrode 16b. The data line 16a crosses the gate line (not shown), thereby defining a pixel region. Next, a passivation layer 17 of an organic material is formed on the data line 16a, and the source and drain electrodes 16b and 16c. The passivation layer 17 covers the TFT xe2x80x9cTxe2x80x9d and has a contact hole 17a exposing the drain electrode 16c. A pixel electrode 18 is formed on the passivation layer 17 at the pixel region and connected to the drain electrode 16c through the contact hole 17a. Here, the pixel electrode 18 of a conductive material such as metal covers the TFT xe2x80x9cTxe2x80x9d and overlaps the data line 16a to improve an aperture ratio. Further, the passivation layer 17 is made of an organic material having a low dielectric constant to prevent signal interference between the pixel electrode 18 and the data line 16a. 
A black matrix 22 is formed on an inner surface of the second substrate 21. A color filter layer 23a, 23b and 23c having red, green and blue colors are formed on the black matrix 22. A common electrode 24 of a transparent conductive material is formed on the color filter layer 23a, 23b and 23c. Here, one color of the color filter layer 23a, 23b and 23c corresponds the pixel electrode 18 and the black matrix covers an edge of the pixel electrode 18. Since the pixel electrode 18 of an opaque material covers the TFT xe2x80x9cTxe2x80x9d, the black matrix 22 can overlap only the edge of the pixel electrode 18.
A liquid crystal layer 30 is interposed between the pixel electrode 18 and the common electrode 24. Further, orientation films (not shown) that determine an initial alignment state of liquid crystal molecules are formed on the pixel electrode 18 and the common electrode 24, respectively.
As mentioned above, the reflective LCD device displays images by reflecting an incident light at the pixel electrode of a high reflective material. Therefore, the reflective LCD device can operate for a longer time without exchanging a battery because power consumption is reduced.
Since the related art reflective electrode has a flat surface, light is reflected as if the reflective electrode is a mirror. This phenomenon is referred to as a mirror reflection. Therefore, the brightness is higher only along any reflection direction depending on Snell""s Law of Refraction. When incident light is reflected on a reflective display according to a position of a light source, the brightness is low along a normal direction of an LCD device. Another phenomenon that occurs is the light glare effect. This happens when a high-intensity external light source is reflected on a liquid crystal display panel. The displayed image is poor due to the glare that occurs as viewed by an observer due to the reflection of light. To increase the brightness along the normal direction and decrease the light glare effect on an LCD device, a reflective electrode of an uneven shape and a front scattering film are suggested.
FIG. 2 is a schematic cross-sectional view of a related art reflective LCD device using a front scattering film. In FIG. 2, a front scattering film 40 is disposed on an outer surface of a second substrate 21. However, an image blurring phenomenon due to back scattering at the front scattering film 40 degrades a display efficiency of the reflective LCD device.
FIG. 3 is a schematic cross-sectional view of a related art reflective LCD device using a reflective plate of an uneven shape. In FIG. 3, a surface of a pixel electrode 18 that is a reflective plate has an uneven shape by forming a passivation layer 17 that has an uneven surface. Accordingly, a brightness along a normal direction of the reflective LCD device increases by changing a reflection angle of light.
A slanting angle of the uneven shape may be about 10xc2x0 so that light can be reflected along the normal direction of the reflective LCD device. However, a process of forming the uneven shape is a complicated process and has a low repeatability. The uneven shape of the passivation layer is initially formed to have a square shape. Subsequently, the passivation layer is cured to form a round shape. Uniform curing of the entire area of the passivation layer is difficult because it is dependent on the curing conditions. The curing temperature may range from about 100xc2x0 C. to about 200xc2x0 C. As a result, the uneven shape is not uniform throughout the entire area of the passivation layer. It is difficult to increase a brightness of a reflective LCD device even using a reflective electrode of an uneven shape due to a smaller effective scattering area of the light on the surface of the substrate. Moreover, since the pixel electrode is made of a metallic material and the common electrode is made of a transparent conductive material, a flicker occurs due to a work function difference between the pixel electrode and the common electrode.
Accordingly, the present invention is directed to a liquid crystal display device that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide a liquid crystal display device having a high brightness along a main viewing angle and a minimized flicker, and a fabricating method thereof.
Another advantage of the present invention is to provide a liquid crystal display device where brightness along a main viewing angle is high and a misalignment of the upper and lower substrates is prevented, and a fabricating method thereof.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a liquid crystal display device includes: first and second substrates facing and spaced apart from each other; a gate line and a data line on an inner surface of the first substrate, the gate line and the data line crossing each other and defining a pixel region; a thin film transistor connected to the gate line and the data line, the thin film transistor having a gate electrode, an active layer, and source and drain electrodes; a passivation layer covering the gate line, the data line and the thin film transistor; a reflective plate of an opaque material on the passivation layer at the pixel region; a scattering layer on the reflective plate, the scattering layer having a contact hole exposing the drain electrode through the passivation layer; a pixel electrode of a transparent conductive material on the scattering layer at the pixel region, the pixel electrode being connected to the drain electrode through the contact hole.
The liquid crystal display device further includes a black matrix on an inner surface of the second substrate, the black matrix covering an edge of the pixel electrode; a color filter layer on the black matrix, the color filter layer having red, green and blue colors; a common electrode on the color filter layer; and a liquid crystal layer interposed between the pixel electrode and the common electrode.
In another aspect of the present invention, a liquid crystal display device includes: first and second substrates facing and spaced apart from each other; a gate line and a data line on an inner surface of the first substrate, the gate line and the data line crossing each other and defining a pixel region; a thin film transistor connected to the gate line and the data line, the thin film transistor having a gate electrode, an active layer, and source and drain electrodes; a passivation layer covering the gate line, the data line and the thin film transistor; a reflective plate of an opaque material on the passivation layer at the pixel region; a scattering layer on the reflective plate; a color filter layer on the scattering layer, the color filter layer having red, green and blue colors, the color filter layer having a contact hole exposing the drain electrode through the passivation layer and the scattering layer; a pixel electrode of a transparent conductive material on the color filter layer at the pixel region, the pixel electrode being connected to the drain electrode through the contact hole.
The liquid crystal display device further includes a black matrix on the scattering layer, the black matrix overlapping the reflective plate; a common electrode on an inner surface of a second substrate; and a liquid crystal layer interposed between the pixel electrode and the common electrode.
In another aspect of the present invention, a fabricating method of a liquid crystal display device includes: forming a gate line and a data line on a first substrate, the gate line and the data line crossing each other and defining a pixel region; forming a thin film transistor connected to the gate line and the data line, the thin film transistor having a gate electrode, an active layer, and source and drain electrodes; forming a passivation layer covering the gate line, the data line and the thin film transistor; forming a reflective plate of an opaque material on the passivation layer at the pixel region; forming a scattering layer on the reflective plate, the scattering layer having a contact hole exposing the drain electrode through the passivation layer; forming a pixel electrode of a transparent conductive material on the scattering layer at the pixel region, the pixel electrode being connected to the drain electrode through the contact hole.
The fabricating method further includes forming a black matrix on a second substrate, the black matrix covering an edge of the pixel electrode; forming a color filter layer on the black matrix, the color filter layer having red, green and blue colors; forming a common electrode on the color filter layer; attaching the first and second substrates, the pixel electrode and the common electrode facing to each other; and injecting a liquid crystal material into a space between the pixel electrode and the common electrode.
In another aspect of the present invention, a fabricating method of a liquid crystal display device includes: forming a gate line and a data line on a first substrate, the gate line and the data line crossing each other and defining a pixel region; forming a thin film transistor connected to the gate line and the data line, the thin film transistor having a gate electrode, an active layer, and source and drain electrodes; forming a passivation layer covering the gate line, the data line and the thin film transistor; forming a reflective plate of an opaque material on the passivation layer at the pixel region; forming a scattering layer on the reflective plate; forming a color filter layer on the scattering layer, the color filter layer having red, green and blue colors, the color filter layer having a contact hole exposing the drain electrode through the passivation layer and the scattering layer; forming a pixel electrode of a transparent conductive material on the color filter layer at the pixel region, the pixel electrode being connected to the drain electrode through the contact hole; forming a common electrode on a second substrate; attaching the first and second substrates, the pixel electrode and the common electrode facing to each other; and injecting a liquid crystal material into a space between the pixel electrode and the common electrode.
In another aspect of the present invention, a liquid crystal display device, comprises: first and second substrates facing and spaced apart from each other; a gate line and a data line on an inner surface of the first substrate, the gate line and the data line crossing each other and defining a pixel region; a thin film transistor connected to the gate line and the data line, the thin film transistor having a gate electrode, an active layer, and source and drain electrodes; a passivation layer covering the gate line, the data line and the thin film transistor; a reflective plate of an opaque material on the passivation layer at the pixel region, the reflective plate having a transmissive portion; a scattering layer on the reflective plate, the scattering layer having a contact hole exposing the drain electrode through the passivation layer; and a pixel electrode of a transparent conductive material on the scattering layer and the passivation layer at the pixel region, the pixel electrode being connected to the drain electrode through the contact hole.
The liquid crystal display device further comprises a transmissive portion which includes a hole wherein a portion of the pixel electrode is formed in the hole below the reflective plate. The transmissive portion is formed by etching a portion of the passivation layer and the scattering layer corresponding to the transmissive portion.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.